1. Field of the Invention
The present invention relates to an ink set, and more specifically to an ink set which can be suitably used for an ink set for inkjet recording.
2. Discussion of the Related Art
Inkjet recording is a recording system for forming characters or images, comprising directly jetting ink droplets from very fine nozzles to a recording medium, and depositing the ink droplets on the recording medium. This system has some advantages such that not only the device shows excellent operability at a low level of noise, but also the coloration is facilitated and plain paper can be used as a recording medium. Therefore, this system has been widely used in recent years.
As the ink for inkjet recording, water-based inks have been widely used from the viewpoint of tractability. As a water-based colorant used in the inks, water-soluble dyes have been mainly used from the viewpoints of jetting reliability and coloration. However, there are some defects in the water-based ink containing a water-soluble dye such that storage properties of the printouts, such as water resistance, light fastness and durability would be impaired.
Therefore, recently, a pigment-containing colorant has been gradually used.
However, as is distinct from a dye-containing colorant in which the dye is uniformly dissolved in an ink, the pigment exists ununiformly as particles having a given size in the ink. Therefore, the pigment-containing colorant causes some problems such that the dispersion stability of the pigment-containing colorant is lowered, and that ink clogging in fine nozzles is apt to be generated when the ink is used for inkjet recording. Therefore, in order to improve dispersion stability and prevent ink clogging in the fine nozzles, there have been reported many techniques for controlling the average particle diameter and particle size distribution of a pigment-containing colorant (Japanese Patent Laid-Open Nos. Hei 3-163175, Hei 8-218015, Hei 8-295837, Hei 10-67958, and the like).
However, there arise some problems such that clear images cannot be satisfactorily formed when these pigment-containing colorants are used, although the dispersion stability is improved and ink clogging is prevented in the nozzles. Usually, an ink set comprising a black ink, a yellow ink, a magenta ink and a cyan ink has been used in a printer for inkjet recording for forming fixed images. When a fixed image is formed on a recording medium having a smooth surface with a black ink and color inks having a controlled average particle diameter and particle size distribution as mentioned above, there exist an area having high gloss and an area having low gloss in the different color regions, so that the image quality tends to be impaired.
An object of the present invention is to provide an ink set which gives a printout showing uniform gloss even when the ink is printed on a medium having a smooth surface. Another object of the present invention is to provide an ink set for inkjet recording showing high gloss and being excellent in water resistance, rubbing resistance and high-lighter fastness, nevertheless the ink is a water-based ink.
These and other objects of the present invention will be apparent from the following description.